The overall goal of this grant is to elucidate the physiological mechanisms by which short-term changes in food intake lead to changes in the central neural drive to the reproductive axis in primate species. Brief periods of fasting (i.e., one to two days) lead to a significant suppression of LH, FSH and testosterone secretion in adult male rhesus monkeys and men. Subsequent refeeding of monkeys after a brief period of fasting leads to a rapid and dramatic increase in LH and testosterone secretion within the first hour after meal intake. Using the experimental paradigms of fasting and refeeding the applicant proposes to: 1) identify neuronal systems which may mediate the changes in LH secretion caused by fasting and refeeding. Experiments will examine the role of three specific neural systems in mediating nutrition-induced changes in LH secretion; the vagus nerves, noradrenergic pathways, and NPY-containing neurons. She further proposes to identify other central neural systems activated by fasting and refeeding by determining the transient expression of cFos and Fos related antigens (FRAs) in identified neuronal populations by using in situ hybridization and immunocytochemical techniques; 2) determine the role of insulin and T3 in causing the suppression of LH secretion during fasting and the restoration of LH secretion during refeeding. 3) determine the extent to which the diurnal pattern of LH secretion in the male rhesus monkey is determined by the pattern of daily food intake, and the timecourse with which changes in the pattern of food intake modify the pattern of LH secretion.